This invention relates to surgical instruments and associated methods of use. More particularly, this invention relates to the use of ultrasound energy in surgical treatments. The invention contemplates method and apparatus for reducing undesirable tissue damage at an operative site. The invention may be used in neurosurgery and general surgery such as liver resection, or in the treatment of wounds, warts or other lesions, wrinkles or skin disease. Alternatively the invention may be used in laparoscopy.
Over the past 30 years, several ultrasonic tools have been invented which can be used to ablate or cut tissue in surgery. Such devices are disclosed by Wuchinich et al. in U.S. Pat. No. 4,223,676 and Idemoto et al in U.S. Pat. No. 5,188,102.
In practice, these surgical devices include a blunt tip hollow probe that vibrates at frequencies between 20 kc and 100 kc, with amplitudes up to 300 microns or more. Such devices ablate tissue by either producing cavitation bubbles which implode and disrupt cells, by generating tissue compression and relaxation stresses (sometimes called the jackhammer effect) or by other mechanisms such as micro streaming of bubbles in the tissue matrix. The effect is that the tissue becomes liquefied and separated. The fragmented tissue becomes emulsified with an irrigant solution. The resulting emulsion or slurry of tissue debris is then aspirated from the site. Bulk excision of tissue is possible by applying the energy around and under an unwanted tissue mass to separate it from the surrounding structure. The surgeon can then lift the separated tissue mass out using common tools such as forceps.
The tubular probe is excited by a vibratory energy source or transducer of either the piezoelectric or magnetostrictive type that transforms an alternating electrical signal within the frequencies indicated above into a longitudinal and/or transverse vibration. When the probe is attached to the transducer, the two become a single element with series and parallel resonances. The designer will try to tailor the mechanical and electrical characteristics of these elements to provide the proper frequency of operation. Most of the time, the elements will have a long straight axis and an operative tip truncated in a plane perpendicular to the long axis. This is done for simplicity and economic considerations. In almost all applications, whether medical or industrial, such an embodiment is practical and useful.
Therefore, it was desired to provide a probe that can be mated to an ultrasonic surgical aspirator that increases the efficiency of emulsification, does not heat up the operative site and lowers the time of operation.
Ultrasonic ablation tools need to be driven at high excursion levels, i.e., high vibrational amplitudes in order to effectively remove unwanted tissue. Once this tissue is removed, the high amplitudes can lead to higher pain perception on the part of the patient and can also lead to destruction of viable tissue such as nerve tissue if the operator is not careful.